Method of manufacture of iodine cycle incandescent lamps



Dec. 8, 1964 3,160,454

E. G. ZUBLER ETAL METHOD OF MANUFACTURE OF IODINE CYCLE INCANDESCENT LAMPS Filed April 2, 1965 lnven tovs: Edward G.ZU1I)LT' Fved A. Mosbg b9 fi If Theiw- A L' L' vneg area. but is caused by an excess of oxygen, removes tungsten United States Patent 3,166,454 7 METHOD OF MANUFACTURE 6F HGDDIE CYQLE HNQANDESCENT LAMPS Edward G. Zubler, Chagrin Falls, and Frederick A. Mosley, Cleveland, ()liio, assignors to General Electric Company, a corporation of New York Filed Apr. 2, 1963, Ser. No. 27ti,5ii5 10 Claims. (Cl. 31621) This invention relates generally to electric incandescent lamps comprising a tungsten filament sealed in a bulb or envelope of light-pervious material containing a filling of inert gas, and more particularly to so-called iodine-cycle lamps which contain a small proportion of iodine vapor which makes possible operation of the lamp at a high temperature and efiiciency for a long useful life with virtual freedom from blackening of the bulb throughout life. This application is a continuationin-part of our application Serial No. 138,939, filed September 18, 1961, now abandoned.

The blackening of the bulbs of ordinary incandescent lamps is the result of sublimation or volatilization of the filament which increases with filament temperature. Although the etficiency of a filament increases very rapidly with increasing temperature, the resultant blackening places a practical limitation on the temperature at which it may be operated and still have a reasonable life. The effect of such bulb blackening is minimized to an appreciable extent by employing bulbs of comparatively large size to distribute the blackening over a large area and also by the presence of an inert gas such as nitrogen, argon, krypton, xenon etc to minimize filament vaporization. I

In the iodine cycle lamp, such as disclosed and claimed in US. Patent No. 2,883,571, Fridrich et -al.,. such bulb blackening is virtually eliminated by employing a relatively small compact bulb and adding a small quantity of iodine vapor to the gas filling in the bulb. The iodine functions as a regenerative getter in association with the tungsten filament by combining with evaporated tungsten at the hot bulb Wall to form tungsten iodine which migrates to the vicinity of the hot tungsten filament where it is dissociated and the tungsten is returned to the filament. The tungsten-iodine cycle operates throughout the life of the lamp, which may be hundreds or thousands of hours, to keep the bulb walls free of blackening.

As pointed out in the aforesaid Patent 2,883,571, the iodine cycle performs effectively provided the lamp is kept free of impurities. One such impurity is iron which is normally present in the tungsten filament. However, the iron content can be kept to a safe limit, preferably not more than about .O()2% by weight, by etching the filament in suitable acids to remove excess iron which is otherwise evaporated during. lamp operation to form a deposit on the bulb wall which combines with the iodine to form iron iodide and, thereby destroy the regenerative cycle.

Besides blackening caused by normal thermal vaporization of the tungsten filament, and which is counter-acted by proper functioning of the iodine cycle, there is -another problem known as cycling. There are two types of cycling which may be encountered and which lead to short lamp life. One is the rather well known water cycle wherein water vapor reacts with the tungsten filament to form tungsten oxide and hydrogen whereby tungsten is removed from a hot area and deposited on a'cooler The other, which operates like the water cycle from a relatively cool area and deposits item a hotter area. The result is erosion of the tungsten filament to a point where it burns through. In order to obtain lamps of long life, careful and prolonged baking at very high ice temperature was required to minimize the proportion of failures due to cycling. Various getters, such as tantalum etc. are employed in ordinary incandescent lamps to break up the water cycle by tying up the oxygen or hydrogen or both. However, such getters cannot be used in iodine cycle lamps because of reaction withiodine and resultant blackening.

It is therefore an object of the invention to provide an improved method of manufacture of iodine cycle lamps which will still further minimize cycling and blackening and which will avoid the necessity for prolonged high temperature treatment.

in accordance with the invention, it has been found that materially improved results are obtained by employing a procedure revolving as essential steps energization of the filament with an atmosphere in the lamp comprising a gaseous hydrocarbon and iodine vapor and preferably also an inert gas, after which the lamp is evacuated and filled with a final filling of inert gas, iodine vapor and a small quantity of oxygen. Further improved results may be obtained by an additional initial step of energizing the filament with a reducing atmosphere of hydrogen in the lamp followed by'evacuation prior to the introduction of the gaseous hydrocarbon and iodine. The lamp gfi y also desirably be baked before introducing the final ing. Further features and advantages of the invention will appear from the following detailed description and from the drawing which is a side view of a form of lamp processed in accordance with the invention.

Referring to the drawing, the lamp shown therein for purposes of illustration is of the type disclosed and claimed in Patent 2,8835 71Fridrich et al., the disclosure of which is incorporated herein by reference. The lamp comprises a tubular bulb or envelope 1 of light pervious material such as glass or quartz having its ends compressed to form flattened press or seal portions 2 in which are hermetically sealed and embedded the lead-in conductors each comprising an outer section 3 of molybdenum wire, an intermediate section 4 of molybdenum foil, and an inner section 5 preferably of tungsten. An axially extending filament 6 of tungsten wire is connected at its ends to the inner end portions 5 of each lead wire. In an elongated lamp, as illustrated herein, the filamentfi is supported intermediate its ends by tungsten wire spirals 7 eugageable with the inner Wall of the bulb l. The bulb 1' contains a filling of inert gas such as argon, krypton or xenon at a substantial pressure, for example argon at a pressure of some 600 to 30,000 mm. Hg. or more, anda small quantity of iodine, preferably between about .01

and l micromole per cc. of bulb volume,to which is added a small quantity, less than 1 mm. Hg, of oxygen.

Prior to assembly of the filament 6 into the bulb l, it

be held to an amount below about. 002% by weight, The filament'is also preferably heated in a hydrogen furnace to degas and set it.

After sealing the assembly of filament 6, leads 3, 4, and supports 7 into the bulb l, as an optional "first step the lamp is evacuated and'filled with hydrogen through the exhaustltube indicated at 8, and the filament 6 is en minutes, for example four minutes, Energizing the fila- The hydrogen treatment also cleans up oxides on the filament, lead wires and supports. The filamentfois then de-energized and the bulb-1 is evacuated; somaor the a oxygen is removed as water vapor. However some of the oxygen is not removed; it may remain as water absorbed in the bulb wall or as tungsten oxide on the bulb wall.

After evacuation, the lamp is then filled with small quantities of a hydrocarbon gas and iodine vapor. In order to hold down vaporization of tungsten from the filamerit, the lamp is at-this time also filled with an inert gas preferably at a pressure exceeding 50 mm. Hg, for example several hundred mm. Hg. 'It may, for example, be filled with 600 mm. Hg of argon containing less than 1% by volume of hydrocarbon gas, for example about 3 to 5 mm. Hg partial pressure of methane. The iodine may be at a partial pressure of a few mm. Hg. The filament is then energized, preferably to a degree sufficient to heat the wall of the bulb 1 to a temperature of at-least 250 C. for about four minutes; usually the filament will be energized at its full normal operating voltage or even higher. It is believed that in this step the methane is decomposed to carbon and hydrogen. There are therefore elements present in the lamp which can produce a water cycle, an oxygen cycle and an iodine cycle. The carbon, having a higher afiinity for oxygen than does the hydrogen or tungsten, will react with the oxygen and Water vapor to form CO and CO while the hydrogen remains as free hydrogen and hydrogen iodide. At the operating temperature of the lamp, enough iodine is available, as free iodine or by decomposition of hydrogen iodide, to allow the tungsten-iodine cycle to function and thereby keep the bulb wall clean. In this step the excess oxygen and water vapor are removed by the formation of CO and CO the hydrocarbon gas providing a convenient method of introducing carbon into the lamp. 7

The filament is then de-energized and the lamp is evacuated to remove the C0, C H and HI formed in the preceding step. In order to further assure the re} moval of residual gases, thelamp may be baked out under vacuum, for example at about 700 or 800 C. for about three minutes. I

The lamp is then filled with its final filling of inert gas, for example about 600 to 1500 mm. Hg of pure argon, about 0.3-0.5 mm. Hg of oxygen, and a small quantity of iodine vapor, for example about mm, and theexhaust tube 8 is sealed or tipped off as indicated at 9.

The iodine cycle will operate in a vacuum, that is without the inert gas in the final filling. However, lamp life is materially increased by the presence of the inert gas.

It isimportant that throughout the sequence of treatments in hydrogen (when used) and in methane and final filling, the interior .of the lamp not be exposed to :-air. As compared with ordinary lamp-making techniques which, in the absence of a costly rigorous baking schedule, may result insome 25 to 50% of defective lamps, the process described above has reduced the proportion of defective lamps to about 1 or 2%. I

While it was proposed many years ago to add methane to the final gas filling of ordinary incandescent lamps inorder to overcome the effects of water vapor, to the best of our knowledge it has not been 'usedyin commercial At any rate, the addition of methane, even inv d deposited thereon, or to interference with proper functioning of the iodine cycle.

The role of the oxygen in the final fill gas is not fully understood. However, tests have shown that. it is necessary in order to maintain the lamp clean. It may be that the oxygen is either tyingup impurities which remain in the filament or other parts of the lamp, or it is acting as a catalyst in promoting the formation of tungsten iodide. In either case, it appears that if enough oxygen is added to combine with a maximum quantity of impurities, and the quantity of oxygen is not in excess of about 0.5 mm., the lamp remains clean.

It will be evident that whereas reference has beenmade particularly to methane as a preferred hydrocarbon gas for the methane treatmen other hydrocarbon gases may be employed, particularly those containing no oxygen, such as acetylene, naphthalene vapor, anthracene vapor, etc.

What we claim as new and desire to'secure by Letters Patent of the United States is:

1. In the manufacture of an incandescent lamp of the iodine-cycle type comprising a sealed bulb of light-per- 'vious material containing atungsten filament, the steps which comprise evacuating the bulb and filling itwith a gaseous hydrocarbon at a pressure of a few millimeters of mercury and a small quantity of iodine; energizing the filament to heat it to a temperature sufiicient to decompose the hydrocarbon -gas while heating the-bulb wall to a temperature of at least 250 -C.; evacuatingthe bulb;

filling the bulb with a final gas filling of a mixture of inert gas, oxygen at a partial pressure in the approximaterange of 03 0.5 mm. Hg and a small quantity of iodine; and sealing off the bulb.

2. The manufactureas set forth in claim 1 including, prior to the step of evacuating the bulb and filling it with gaseoushydrocarbon, thestep of filling the bulb with hydrogen and energizing the filament to a temperature of at leastabout i000 C. for at least a few minutes.

3. The manufacture as setforth in claim 1 wherein, during the step of filling'the bulb with a gaseous'hydrocarbon and iodine, there is added an inert gas at a pressure of at least about 50mm. Hg.

4. The manufacture as set forth in claim 1 including,

prior to the step or" evacuating the-bulb and fillingiit with at leastabout' 1000" .C. for at least a few minutes,,and

also wherein, during the step of filling the bulb with a gaseous hydrocarbon and iodine, there is addedan inert gas at a pressure of at least about 50 mm. Hg.

'5. The manufacture asset forth in claim 1 wherein the .said gaseous hydrocarbon is methane.

6. The manufacture as set forth in claim 1 wherein the said gaseous hydrocarbon is methane at a pressure in the range of about 3 to 5 mm. Hg.

7. The manufacture as set forth in claim 1 including,

. prior to the step of filling the bulb with the final gas fill- "ing, the step of baking outythe bulb under vacuum at a a 1 temperature in the order of 700-800 C. a

vapor ofiodine cycle lamps results in heavy blackening or f in cycling. It may be that carbon deposits on the bulb wall as a film which interferes with functioning of the iodine cycle. In other words carbon, improperly employed, can be highly detrimental to the operation of an iodine cycle lamp, leading to sagging of the filament when 8. The manufacture as set forth in'claim 2 wherein the said gaseous hydrocarbon is methane.

9. The manufacture as set forth'in claim 3 wherein the said gaseous hydrocarbon is methane;

10. The'manufactureas set forth-in claim 4 wherein the said gaseous hydrocarbon is-methane.

V I No references cited. 

1. IN THE MANUFACTURE OF AN INCADESCENT LAMP OF THE IODINE-CYCLE TYPE COMPRISING A SEALED BULB OF LIGHT-PERVIOUS MATERIAL CONTAINING A TUNGSTEN FILAMENT, THE STEPS WHICH COMPRISES EVACUATING THE BULB AND FILLING IT WITH A GASEOUS HYDROCARBON AT A PRESSURE OF A FEW MILLIMETERS OF MERCURY AND A SMALL QUANTITY OF IODINE; ENERGIZING THE FILAMENT TO HEAT IT TO A TEMPERATURE SUFFICIENT TO DECOMPOSE THE HYDROCARBON GAS WHILE HEATING THE BULB WALL TO A TEMPERATURE OF AT LEAST 250*C.; EVACUATING THE BULB; FILLING THE BULB WITH A FINAL GAS FILLING OF A MIXTURE OF INERT GAS, OXYGEN AT A PARTIAL PRESSURE IN THE APPROXIMATE RANGE OF 0.3-0.5 MM. HG AND A SMALL QUANTITY OF IODINE; AND SEALING OFF THE BULB. 